As energy prices are increasing due to depletion of fossil fuels and interest in environmental pollution is escalating, the demand for environmentally-friendly alternative energy sources is bound to play an increasing role in the future. Thus, research into techniques for generating various powers, such as nuclear energy, solar energy, wind energy, and tidal power, is underway, and power storage apparatuses for more efficient use of the generated energy are also drawing much attention.
In particular, the demand for batteries as energy sources is rapidly increasing as mobile device technology continues to develop and the demand for the mobile devices continues to increase. Accordingly, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch type secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, on the other hand, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, which exhibit high energy density, discharge voltage, and output stability, is very high.
In addition, secondary batteries may be classified based on the structure of an electrode assembly having a structure in which a positive electrode and a negative electrode are stacked in the state in which a separator is interposed between the positive electrode and the negative electrode. For example, the electrode assembly may be configured to have a jelly-roll (wound) type structure in which a long sheet type positive electrode and a long sheet type negative electrode are wound in the state in which a separator is disposed between the positive electrode and the negative electrode or a stacked type structure in which pluralities of positive electrodes and negative electrodes each having a predetermined size are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes. In recent years, in order to solve problems caused by the jelly-roll type electrode assembly and the stacked type electrode assembly, there has been developed a stacked/folded type electrode assembly, which is a combination of the jelly roll type electrode assembly and the stacked type electrode assembly, having an improved structure in which predetermined numbers of positive electrodes and negative electrodes are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes to constitute a unit cell, and then a plurality of unit cells is sequentially folded while being placed on a separation film.
In addition, based on the shape of the battery case of each of the secondary batteries, secondary batteries may be classified into a cylindrical battery configured to have a structure in which an electrode assembly is mounted in a cylindrical metal container, a prismatic battery configured to have a structure in which an electrode assembly is mounted in a prismatic metal container, and a pouch type battery configured to have a structure in which an electrode assembly is mounted in a pouch type case made of an aluminum laminate sheet.
Particularly, in recent years, much interest has been taken in a pouch type battery configured to have a structure in which such a stacked or stacked/folded type electrode assembly is mounted in a pouch type battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, easy modification in shape, etc. In addition, the use of such a pouch type battery has gradually increased.
In the above secondary battery, various phenomena and changes occur in electrodes constituting the electrode assembly during the operation of the battery, and the results of real-time observation of the phenomena and changes occurring in the electrodes may be used for basic studies and the diagnosis of the battery and for the improvement in performance of the battery. However, the electrode assembly is mounted in the opaque battery case in a sealed state, and the electrodes constituting the electrode assembly are stacked in the state in which separators are interposed respectively between the electrodes. For these reasons, it is difficult to observe various phenomena and changes occurring in the electrodes during the operation of the battery.
In addition, some additional batteries for experimentation used for observe the electrodes constituting the electrode assembly have been developed. However, the internal structure of the batteries for experimentation is complex, with the result that it is difficult to realize the batteries for experimentation using a conventional secondary battery manufacturing process. In addition, some components of the batteries for experimentation are different from those of conventional secondary batteries. Specifically, electrodes having a coin cell size are used, with the result that it is difficult to realize the same performance as the conventional secondary batteries. For this reason, it is not possible to apply the observed results of the electrodes to the conventional secondary batteries with high reliability.
Therefore, there is a high necessity for technology that is capable of fundamentally solving the above problems.